code: def data():
      """Generates test dataframe for outlier detection"""
      df = pd.DataFrame(
          {
              "a": np.repeat(1.0, 100),
              "b": np.arange(0.0, 100.0, 1.0),
              "c": np.tile([1.0, 2.0, 3.0, 4.0], 25),
              "d": np.repeat(1.0, 100),
          }
      )
      df.loc[2, "b"] = 100.0  # z-score 1.74
      df.loc[4, "c"] = 6.0  # z-score 2.95
      df.loc[6, "d"] = 100.0  # z-score 9.90
      return df
  
file_path: greykite/greykite/tests/sklearn/transform/test_zscore_outlier_transformer.py
imports: import numpy
  import pandas
  import pytest
  from sklearn.exceptions import NotFittedError
  from testfixtures import LogCapture
  from greykite.common.constants import LOGGER_NAME
  from greykite.common.python_utils import assert_equal
  from greykite.sklearn.transform.zscore_outlier_transformer import ZscoreOutlierTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: data() and returns: df